IO-520: FileUtilsTestCase#testContentEqualsIgnoreEOL fails on Windows

exclude .dat files used by tests related to line-endings from git line-ending normalization
diff --git a/.gitattributes b/.gitattributes
index a354649..288cfe5 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -22,3 +22,6 @@
 *.css    text
 *.js     text
 *.sql    text
+
+# Exclude test files for line-ending related tests from normalization (IO-520)
+*.dat binary